1. Field of the Invention
The present invention relates generally to substance delivery devices. Specifically, the invention relates to an injection device and method that incorporates microneedles and skin tensioning systems for providing an optimal interface for an injection.
2. Description of the Related Art
Currently, various devices have been proposed for monitoring, sampling and delivering substances transdermally. Although the prior subcutaneous delivery methods using a needle for delivering pharmaceutical agents and drugs are effective for many applications, the pain normally induced by the needle has prompted the development of less painful delivery methods. Transdermal delivery is one method of avoiding the pain caused by subcutaneous sampling and delivery using a needle.
In recent years there has been an increased interest in microneedles for sampling and for the transdermal delivery of drugs and other substances. Microneedles are short (generally 3 mm or less) needles that can pierce the skin to a depth wherein a substance can be delivered into the epidermis, such that the substance can be readily absorbed by the body. An advantage of the use of microneedles is their ability to penetrate the outermost layers of the skin with only minor discomfort to the patient, as compared to a standard needle.
As known to those skilled in the art, the skin is made up of several layers, with the upper composite layer being the epithelial layer. The outermost layer of the skin is the stratum corneum, which has well known barrier properties to prevent molecules and various substances, including most pharmaceutical agents, from entering the body, and further preventing analytes from exiting the body. The stratum corneum is a complex structure of compacted keratinized cell remnants having a thickness of about 10-30 microns.
Various methods of delivering drugs through the skin typically form micropores or cuts through the stratum corneum. By penetrating the stratum corneum and delivering the drug to the skin in or below the stratum corneum, many drugs can be effectively administered. The devices for penetrating the stratum corneum generally include a plurality of microneedles or blades having a length to penetrate the stratum corneum without passing completely through the epidermis. Examples of these devices are disclosed in U.S. Pat. No. 5,879,326 to Godshall et al., in U.S. Pat. No. 5,250,023 to Lee et al., and in WO 97/48440, the entire contents of each being incorporated herein by reference.
Accordingly, microneedles have been used with some success for various substances that are effective when delivered transdermally or intradermally. However, many of the prior microneedle devices that are currently available are not able to penetrate the skin uniformly across the microneedle surface, thereby reducing the surface area available for delivery of the substance. That is, skin is generally elastic and the skin often deforms before the microneedles penetrate. In some instances, the microneedles deform the skin but do not penetrate the skin to a depth sufficient to deliver a drug.
For example, some current microneedle devices are rigid holders that retain a microneedle in the skin by an adhesive or tape on an area of the device some distance from the needle. These devices poorly compensate for the topography of the skin and may not precisely insert the needle the proper distance.
Numerous other methods and devices have been proposed to enhance the permeability of the skin and to increase the diffusion of various drugs through the skin so that the drugs can be utilized by the body. Typically, the delivery of drugs through the skin is enhanced by either increasing the permeability of the skin, or increasing the force or energy used to direct the drug through the skin.
Yet another proposed solution to the above problems is disclosed in U.S. Pat. No. 6,808,506 to Lastovich et al., the entire contents of which are incorporated herein by reference. The Lastovich patent discloses an apparatus for delivering or withdrawing a substance through at least one layer of the skin. For example, the Lastovich patent discloses a device to deliver a substance to one or two different depths, and specifically, to two different physiological tissue compartments, such as shallow subcutaneous and intradermal. As the skin of a subject has elastic properties that resist penetration by the dermal-access members, the skin can be stretched by a raised first surface area of the device until the skin is taut before the dermal-access members of the device penetrate the skin. A penetrating pressure can then be applied to the device until a first surface area contacts the skin. This promotes uniform penetration of the skin by each of the dermal-access members.
These prior methods and apparatus for the transdermal administration of drugs, however, have exhibited limited success especially in regard to leakage rates. Accordingly, a continuing need exists in the industry for an improved device for delivering substances with minimal leakage rates.